body {
    margin: 0;
    padding: 0;
    font-family: Arial, sans-serif;
    height: 100vh;
}
.body {
    margin-bottom: 60px; /* 空出导航栏的空间 */
}
ul {
    list-style-type: none;
    padding: 0;
    margin: 0;
}
li {
    padding: 10px;
    background-color: #f9f9f9;
    border-bottom: 1px solid #ddd;
}
li a {
    text-decoration: none;
    color: black;
}
li .has_new {
    color: red;
}
.navbar {
    position: fixed;
    left: 0;
    bottom: 0;
    width: 100%;
    background-color: #333;
    overflow: hidden;
}
.navbar a {
    float: left;
    display: inline-block;
    color: white;
    text-align: center;
    padding: 14px 0;
    text-decoration: none;
    width: 50%; /* 平均分布在导航栏上 */
}
#send_message:disabled {
    border: 1px solid lightgray;
    background-color: lightgray;
}
